* Error: Blocks all new windows, even when clicking "open link in new window" or opening a new window from the Firefox main menu! (if enabled global)
* Good to use by putting certain sites on the black-list.
* Minor: When a pop-up was blocked and I click "allow once" via the add-on symbol, it does not open the pop-up, but starts the "all pop-ups allowed for 20 seconds" countdown. If that is what the button does, why change its label to "allow once"?

Result: Simple add-on. Still helps. Will continue using.

* Idea: Implement per-host settings
* Suggestion: Option to block pop-ups / tabs from other hosts than the current